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Frequency
bu14-1 
1/7/08 1:22:21 PM
Journeyman

Is the frequency response of headphones/speakers different to the frequency of CDs for example? Could someone please explain this?

Thanks.

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nickeax 
1/7/08 2:14:10 PM
Banned

Frequency means how often something happens over time. In audio, this is how often the high to low part of a signal repeats or occurs each second. The faster the signal rises and falls, the higher the perceived
pitch of the sound will be.

The frequency of a CD is 44,100 Hertz, meaning that the highest frequency that may be represented by a CD is 44.1KHz. Simply, to digitise sound, a machine will record, as a number, the level of the sound signal at a set number of times per second. This process is known as digital sampling. For a CD, this process is carried out 44,100 times per second, building a graph of data that represents a very close approximation of the original sound, but with numbers. That is a vast simplification, but you get the idea, right?

Frequency response refers to how a piece of gear reproduces a given audio signal. In other words, how accurately do you get out, what you put in? A 'flat' FR means that the input signal is not affected by the gear, frequency wise. And in this case, frequency translates to tone or timbre. Why? Because all sounds have pitch, but they also have 'overtones' which are multiples of the base frequency that gives them their pitch. These overtones are what give different instruments their character and tone.

If a pair of headphones showed a spike in it's upper frequency response range, this would mean sounds coming from the phones would seem to have more treble than they should. Sometimes the FR is 'played around with' to afford more pleasing results than a flat response, but be careful! Microphones are notorious for 'wavy' frequency response graphs!

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stadl 
1/7/08 8:49:11 PM
SuperHero
Titan


The 44.1KHz freqnency of CD is the sampling rate of CDs. This is the number of times per second it changes the output signal voltage - think of it as how many times it plots a point.

The maximum frequency that can be correctly reproduced by a 44.1kHz (44100Hz) sampling rate is less than half that - ie anything up to (but not including) 22050 Hz.

Making this slightly more difficult is that you need to have a low-pass filter that cuts out things greater than that maximum, and these filters are not perfect (ie, they don't allow 22049 at full strength but completely remove signals at 22051) So in reality it's probably somewhere around 20k to 21k that is the maximum frequency output by the audio stage of a CD player - your mileage may vary with the equipment.

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-80 
2/7/08 12:06:05 AM
Banned

Nyquist was the man.

http://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem

CD's were good tech for 1980 but DSD is where it's at now.

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